This invention relates to a thrust supporting structure for a marine propulsion unit and more particularly to an improved construction for transferring forward and reverse driving thrusts from a propeller shaft to the lower unit of a marine propulsion unit.
One well-known form of marine propulsion unit includes a forward/neutral/reverse transmission that is comprised of a driving bevel gear that is enmeshed with a pair of counter rotating driven bevel gears which are, in turn, journaled on a propeller shaft to which a propulsion device is affixed. A dog clutching arrangement selectively couples one of the driven bevel gears for rotation with the propeller shaft to drive an associated watercraft in a forward or reverse direction. A wide variety of thrust taking arrangements have been proposed for transferring driving thrusts from the propeller shaft to the lower, unit and, accordingly, to the associated watercraft.
One form of thrust taking arrangement provides a flange integrally on the propeller shaft which is engaged with forward and reverse thrust bearings for transferring forward and reverse driving thrusts from the flange to the lower unit housing. Although this construction has a number of advantages, there are certain disadvantages, particularly in the cost and difficulty of forming a flange integrally with the propeller shaft for transmitting the driving thrusts. If the propeller shaft is made from a machining operation, then there is substantial wastage of material as the shaft is machined to provide the resulting flange. On the other hand, if the propeller shaft is formed as a forging, then the material wastage is avoided, but the cost of manufacturing the forging is rather large because of the successive forging steps required. In addition, with each type of arrangement, it is difficult to insure that the thrust flange is formed at the appropriate location on the propeller shaft.
It is, therefore, a principal object of this invention to provide an improved thrust taking arrangement for the propeller shaft of a marine propulsion unit.
It is a further object of this invention to provide an improved thrust taking arrangement for the propeller shaft of a marine propulsion unit wherein forward and reverse drive thrusts are transmitted from the propeller shaft to the lower unit housing through a flange.
It is a further object of the invention to provide a thrust taking arrangement of the type described in the preceding paragraph wherein the flange need not be formed integrally with the propeller shaft.